1. Field of the Invention
This invention relates to a subterranean well valve employing a flapper valve to open and close a production fluid conduit.
2. Description of the Prior Art
Subsurface safety valves are employed in oil and gas wells to close a production fluid conduit, such as a production tubing string, in the event of an emergency. These safety valves are positioned at downhole locations where they will be unaffected by damage to the wellhead. Conventional downhole safety valves include ball type and flapper type safety valves, each of which can be rotated to open the flow path. Normally both ball type and flapper type safety valves are actuated by axial movement of a shiftable actuator responsive to an increase in control fluid pressure. Conventional flapper type safety valves generally employ an axially movable flow tube which strikes the downstream surface of the closed flapper to cam the flapper open as it rotates about a hinge pin. U.S. patent application Ser. No. 232,473, filed Feb. 9, 1981 now U.S. Pat. No. 4,411,316, discloses a downhole flapper type safety valve actuated by an axially shifting flow tube. The safety valve disclosed therein is a non-equalizing safety valve.
Equalizing safety valves are valves which permit pressure equalization on the upstream and downstream sides of a valve head prior to shifting the valve head to open the primary fluid conduit In many wells a large pressure differential can exist between the relatively greater pressure on the upstream side of a closed valve and the relatively smaller pressure on the downstream side. Conventional ball and flapper type safety valves employ axially shiftable sleeves to open ports either above or below the closed valve head to permit communication with an equalizing flow path bypassing the closed valve.
U.S. patent application Ser. No. 259,767, filed May 1, 1981, and U.S. patent application Ser. No. 350,670, filed Feb. 22, 1982, now U.S. Pat. No. 4,415,036 disclose flapper type safety valves having a centrally located aperture extending through the valve. Valve stems extending through these apertures can be actuated upon downward movement of a flow tube type actuator to permit equalizing flow through the centrally located aperture passing around the shiftable valve stem. Each of these valves requires use of a separate head attached to the valve stem for engagement with the axially shiftable flow tube actuator.
The invention disclosed and claimed herein employs an offset aperture located adjacent the periphery of the flapper type valve having a plug or poppet valve located therein. The poppet valve is in direct axial alignment with the end face of the axially shiftable actuator and an equalizing flow passage is established through the cylindrical poppet valve itself rather than through the aperture extending through the flapper valve head. The poppet valve disclosed and claimed herein forms a metal-to-metal seal with the flapper adjacent the periphery of the flapper sealing surfaces and are not exposed to high velocity equalizing flows.